The speeds are 48, 52, 57, 55, 45, 39, 61, 49, 51 and 43 (in km/hr)
Sum of the speeds
=48+52+57+55+45+39+61+49+51+43=500
Number of motorists whose speeds were taken into account = 10
Average = Sum of all the observationsTotal no. of observations
Average Speed =Sum of the SpeedsNumber of motorists∴Average Speed =50010 =50 km/hr